I've heard some complaints on abcpool's thread about getting messages "pool not providing work fast enough".  I've seen this error myself occasionally.  I figured maybe abcpool is slower than btcguild so I set up an experiment:

I shortened my list from 4 to 2 so now it's abcpool and btcguild and made abcpool the primary.  I seem to be mining on both roughly equally.
I switched the pools so that btcguild is primary and re-ran.  Same result: roughly equal mining on both pools.